Polyalphaolefin: a synthetic hydrocarbon made by joining alpha-olefin molecules such as 1-decene into short chains and hydrogenating the result. PAOs combine high viscosity index, pour points from about -30 C in the heaviest grades to below -60 C in the lightest, strong oxidation stability and low volatility, which makes them the default synthetic for gear, compressor and wide-temperature grease applications. Their weakness is poor solvency for additives and low seal swell, so formulators usually blend in a few percent of ester.
That wind-turbine gearbox runs a PAO 320, don't you dare top it off with mineral gear oil.
Also heard as
- polyalphaolefin
- Group IV
Related terms
Base oil group
Five-group system that sorts base stocks by saturates, sulfur, viscosity index and chemical type.
Ester
Synthetic or natural base oil made from acids and alcohols, valued for solvency, film strength and biodegradability.
Syn
Clipped shop word for synthetic oil or grease, as in syn gear oil or full syn.
Viscosity index
Number showing how little an oil's viscosity changes with temperature; higher means flatter.